Some well-funded pro-Mitt Romney superPACs and other advocacy groups are pulling their TV ad dollars in Pennsylvania and Michigan and are doubling down on efforts in what they consider to be more crucial swing states — such as Florida, Ohio, Iowa and Colorado.

Those are states where President Obama has also been spending considerable time campaigning lately, but where he's facing a barrage of attack ads from his Republican rival and the conservative superPACs, such as American Crossroads, and nonprofit advocacy groups, like Americans for Prosperity.

In an interview with KUNC in Colorado, Americans for Prosperity president Tim Phillips said decisions about where and when to place ads are always fluid, saying recent polls showing Obama with sizable leads in Michigan and Pennsylvania had little to do with his group's decision.

"It doesn't mean that you wouldn't go back there at some point soon," Phillips said. "Dollars are not endless; you have to make sure that every dollar you spend is in a place where it'll make a difference."

According to The Associated Press, Americans for Prosperity, funded by billionaire brothers Charles and David Koch, and the Karl Rove-backed American Crossroads, have pulled their ads in Michigan and Pennsylvania and are now pouring nearly $13 million into Colorado, Florida, Iowa, North Carolina, New Hampshire, New Mexico, Nevada, Ohio, Virginia, Wisconsin and Minnesota.

Phillips predicted his group's activity would be far less fluid in states like Colorado until the election. Most polls have shown Obama and Romney in a statistical dead heat in the Centennial State.

"This part of the country — Colorado, Nevada, New Mexico — they've been hit pretty hard [economically] and they haven't seen the results from the president's policies," he said. "We think there is enormous opportunity here."

In Colorado this week, Americans for Prosperity wasn't just on the airwaves. The group — and Phillips — brought its "Failing Agenda" bus tour to suburban cities up and down the state's heavily populated Front Range. The group said the tour was meant to highlight what it says are Obama's failed economic policies.

Turnout at the group's event at a park in the south Denver suburb of Centennial was modest. Organizers grumbled because the city wouldn't allow their bus to be parked at the venue itself because the required permits hadn't been secured, leading to some perhaps requisite jokes about excess government regulation.

At least one heckler, who appeared to have been at the park with his children already, shouted pro-Obama words as the event was beginning.

The Obama campaign itself has criticized Americans for Prosperity and the Koch brothers for promoting an agenda that Democrats say would put the interests of corporations in front of progress made on clean energy and environmental protections.

In a statement, DNC spokesman Patrick Rodenbush went further: "This bus tour, funded by the Koch brothers, is just another example of wealthy individuals seeking to buy the election for Mitt Romney to protect their own special interests instead of the middle class," he said.